\section{Conclusion}\label{conclusion}
In this paper, we make the following three key contributions.
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First, we proposed arguably the first RFID estimation protocol for multi-category tags.
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The key idea is to use Manchester coding to achieve simultaneous estimation of the tags in multiple categories.
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Second, we propose the optimization technique of adaptive partitioning to address the issue that category sizes may have large variances.
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The key idea is to group categories of similar sizes together and execute our estimation protocol for each group separately.
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Third, we conducted extensive experiments to evaluate the proposed protocols.
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The experimental results show that our optimized multi-category RFID estimation protocol significantly outperforms solutions that can be adapted from prior protocols that were not designed for multi-category RFID estimation.